Bulk liquid material is transported by tractor-trailer combinations in which the bulk liquid material is loaded into a container of the trailer. For example, the container can be a tank built into the trailer that is filled with a liquid bulk liquid material. Special precautions must be taken when loading liquid bulk liquid materials that are hazardous materials and substances such as flammable liquids, corrosives, or a cryogenic substance such as liquid oxygen, liquid nitrogen or other liquefied gases.
In trailers that have an air ride suspension, the tank or other container of the trailer is supported by a pneumatic air suspension system having air bags to support the container on the axles of the trailer. The air bags are supplied with compressed air that is generated by a compressor powered by an internal combustion engine of the tractor, typically a diesel engine. The pneumatic suspension system has a pneumatic circuit which supplies the air from the compressor to the air bags. Among other known features of such a pneumatic circuit are self-leveling valves that are provided for each set of the air bags to ensure that the container is maintained at a level attitude and at a predetermined ride-height. In this regard, in a trailer having two axles, there would be four air bags, two over each axle and on either side of the trailer chassis.
It is safety critical that the weight of bulk hazardous materials being loaded into the trailer does not exceed a predetermined weight that would overload the trailer. Scales, while being the most accurate way to load bulk liquid materials into trailers, are expensive devices to acquire and maintain and in any case, are not always available during loading operations. Thus, loading trailers to a desired weight, on a consistent basis, when a scale is not available is an on-going challenge. When product is inconsistently loaded into the trailer, distribution inefficiencies can arise that will equate to a revenue loss, product waste and related costs attached to under or over-loading trailers during the filling process.
It has long been known that the weight of a trailer can be equated to the pressure within air bags of a pneumatic suspension system. For example, in U.S. Pat. No. 4,832,141, pressure is measured within an air bag of a pneumatic suspension system via a transducer that is connected to a read-out device located in the vehicle to display the weight of the load. Similarly, U.S. Pat. No. 6,025,563 discloses an apparatus that utilizes pressure within an air bag to determine the load weight of the trailer in which a calibration signal represented of predetermined load weight limit levels stored within a digital memory and utilized for comparison basis to compare the calibration signal pressure signals preferable to air bag pressure. Indicators are then used to indicate when the load weight is either below or above predetermined load weight limit levels.
The problem with such methods is that they depend upon the tractor engine operating to power the compressor to supply compressed air to the pneumatic suspension system. This of course presents a safety hazard when substances such as gasoline or liquid oxygen are to be carried. However, if the ignition is turned off and the compressor therefore shuts down, as the container of the trailer is loaded with the bulk liquid material, the air stored within a reservoir of the pneumatic system will deplete, resulting in a delay in the air bag lifting process and inaccurate readings and a potentially shifting of the bulk liquid material within the container to prevent maintenance of the container in a level attitude when loading or even afterwards, when the tractor engine is restarted.
In order to overcome these problems, the present invention provides a process for measuring the weight of the container during its filling with the bulk liquid material that allows the tractor engine to be shut down.